This invention relates to plastic film handling and processing equipment, and is more specifically directed to improved plastic film punch equipment for making holes, openings, and/or slits in one or more layers of a plastic film. The invention is more particularly concerned with an improved punch for plastic film which permits a web of film to move continuously past the punching or cutting station, without intermittent start-stop motion, while holes, openings, and/or slits are being formed in the plastic film material.
The equipment that may be associated with which the punch apparatus of this invention may include a bag machine or similar machine in which where the plastic film is prepared for fabrication into bags, protective sleeves, or other plastic film products.
Punches for bag making machines, in which flexible plastic film is cut and/or in which holes or openings are formed in the film, typically have a pneumatic cylinder or other reciprocating device positioned above an apertured backing plate. The web of plastic film is drawn in one direction so that it moves across the backing plate. The cylinder rod carries a cutting head, which may be steel, brass, or in some cases plastic. The profile of the cutting head is the shape of the hole that is to be formed in the plastic film. When the film reaches the position where the hole is to be punched, the film transport motion is stopped, and the hole is punched by actuating the cylinder. A hold-down clamp descends and holds the film in place on the backing plate. The cylinder pushes the head into the film so that it penetrates the film, and enters into an aperture in the backing plate, to cut the desired opening. Then the head rises back up, the hold-down clamp releases the web of film, and the film moves to the place where the next hole is to be formed. Then the process is repeated. The cut-away circles of plastic film, i.e., “slug”, drop into a tube below the apertured backing plate, and can be conducted away, and later recycled or disposed of. Because the cutting head moves strictly vertically, the film has to be stopped momentarily for the cutting operation. If the film were to continue during the time the cutting head has penetrated the plane of the film, then the head would pull the plastic film and would tend to cause undesirable tears and stretches in the film.
The intermittent stopping and starting of the film motion requires additional equipment and controls, and also tends to limit the speed at which the film can be processed in a hole-punching operation. Consequently, the plastic film industry would welcome an effective technique that would form holes in the film, while the film web was in constant motion, but without tearing or stretching the film.